mixin container()
  .container
    if block
      block
mixin row()
  .row
    if block
      block
mixin col(opt)
  -
    var classs=[];
    for(var key in opt){
      var cls = 'col-'+key+'-'+opt[key];
      classs.push(cls);
    }
    classs=classs.join(' ')
  div(class=classs)
    if block 
      block